The acid that is believed to be mainly responsible for the damage of Taj Mahal is

So₂ is the component of classical smog.

Complete reaction of acid rain is

$2S{O}_2+O_2+2H_{2}O\stackrel{}{\to }2H_{2}S{O}_4\left(acidrain\right)$  

BOD value less than 5ppm is considered as clean water and BOD value more than 10ppm is considered as polluted water.

BOD is the amount of oxygen required by bacteria to break down the organic matter present in a certain volume of sample of water.

Veronal is a barbiturate drug and it constitutes an important class of tranquilizers.